The inventory cars aren’t available for sale really. If you tried to buy one, they’d give you a delivery date at the end of November after the first ship is due to arrive (see the shipping thread).
Inventory cars are ‘spare’ ones. Tesla don’t build to order. They just build combinations of cars they think will sell and ship them over. If there is an inventory one that matches your spec, it’s either because they haven’t matched you to it yet, or there’s more than one car that matches your spec, you’ve been matched to one and the spare is going into inventory. As they run through the matching process of cars in the ship to orders, the inventory will increase or decrease with unmatched cars.